We use mouse spermatogenesis as a model system to investigate mechanisms regulating cellular differentiation. The daily production of millions of gametes (sperm) relies on the activity of a small spermatogonial stem cell population that produces committed progenitor spermatogonia that differentiate in response to retinoic acid. It is currently unclear how these mammalian spermatogonial fate decisions are regulated; however, they are critical for maintaining tissue homeostasis, as imbalances cause spermatogenesis defects that can lead to human testicular cancer or infertility.